Switch machines for railway and tramway switches are well known and have considerable advantages.
Particularly in high speed railway lines, switches have relatively long switch points to provide such a wide radius of curvature as to withstand the high speed of the train. Unlike conventional switches, in which a switch machine is provided at the heels of the switch points and an additional switch machine is possibly provided at the frog of the switch points, high speed switches as described hereinbefore have multiple switch machines arranged all along the switch points, to keep the latter in the proper curvature condition as the train passes thereon.
Switch machines have the function of displacing switch points between two switch positions, in which one of the switch points is thrown against the corresponding rail and the other one is moved away from it. The switch point carrier units in switch machines also have latches that automatically lock the points in the thrown position as they reach said thrown position and that are moved to the point releasing condition as soon as the carrier units are actuated to move the thrown switch point away from the corresponding rail. The latches can be of the so-called trailable or non-trailable type, i.e. connections may be provided between point carrier units which allow the train to displace the points as it passes through the switch, thereby releasing said points from position locking latches. Such connections are so adjusted that the train wheels must exert a certain thrust on the switch points, e.g. when the train runs through an unswitched turnout in the direction opposite to the direction of traffic. The wheel progressively wedges between the thrown switch point and the corresponding rail and pushes the switch point away from the rail.
In the non-trailable type, the switch points are fixedly held in the thrown position so that any train passage would have the effect of damaging the carrier units or special weakened portions requiring a predetermined breaking force.
Obviously, the trailability of a switch machine requires higher construction costs; moreover, in switches with very long switch points, trailability is only required for the switch machine/s at the heels of the switch points, whereas in the intermediate portion and at the frog, given a typical train passage situation, as described above, the train wheels do not exert any thrust forces on the switch points.
Other construction parts of the switch point carrier units in the various switch machines are common and substantially identical for all switch machines.
Considering that in high speed applications each switch is required to have a large number of switch machines along its length, there is the need for minimizing switch machine fabrication costs and times.